Field of the invention
The present invention concerns a deflection unit for a television tube having three aligned guns. It also concerns an apparatus and process for adjusting the deflection unit. It can have various applications in the field of large-scale manufacture of deflection units and in the field of assembling deflection units of television tubes intended for use by the general public.
Description of the Prior Art
According to the processes of the prior art, it is known to manufacture magnetic deflection units comprising a line winding and a raster winding, thereby realizing a scanning for generating a high-quality coloured picture. These deflection units achieve, by modelling the magnetic field lines, self-convergence an various corrections to the picture are made which were previously carried out by assistance circuits. However it is necessary to carry out a very precise adjustment of the deflection unit. In fact, this unit comprises, on a conical separator, a ferrite bearing a toroidal winding for raster scanning. A winding in the form of a saddle for line scanning is fixed inside the separator, and the ferrite is mounted movably upon the separator. The deflection unit only functions if:
the two windings are correctly situated with respect to each other; and
the deflection unit itself is correctly situated on the neck of the tube upon which it is mounted.
The adjustment of the deflection unit is conventionally carried out in two operations. The first operation is conducted once the process for manufacturing the deflection unit has been carried out, and the deflection unit is thus stuck in such a way as to secure this adjustment. The second operation is carried out upon mounting of the tube during assembly of the various components.
The major drawback with this process is that it is necessary to utilize a test or trial tube for the first operation in order to display a test pattern. To do this, sampling is carried out by statistical methods using a series of test tubes intended for the first operation. Each test tube presents mean characteristics that allow an adjustment of the deflection unit according to the first operation to be transportable to another tube. However, the selection of the test series is a delicate operation. Each deflection unit is brought, after manufacture, to an adjustment station according to the first operation. An operator places the deflection unit upon the neck of a test tube mounted within a darkroom and links up the connections of the windings of the deflection unit to a test pattern generator. By displaying the test patterns it is possible to measure four convergence defects or faults known as vertical and horizontal amplitudes and vertical and horizontal crossings or intersections. The first operation is performed to reduce these four test pattern defects. The drawbacks are considerable and include
the problem of selecting a test tube;
the necessity of an operator's presence for the visual appreciation of a dimensional fault or defect upon a picture;
the slowness due to the manual character of the handling operations;
the necessity of providing a large number of stations, all similar in character, for adjusting the large-scale production of deflection units and;
the high cost per unit at each station.